Nice custom beamer theme: how to do something like it?

You'll need to create a .sty file and install it like described here: Where to place custom beamer themes

A sweet tutorial about customizing beamer themes (via Wayback Machine):

https://web.archive.org/web/20130724090805/http://www.math.umbc.edu:80/~rouben/beamer/quickstart-Z-H-8.html

You can also find examples to modify: http://latex.simon04.net/

Here's a particularly good one (via Wayback Machine):

https://web.archive.org/web/20151005203517/http://www.matdat.life.ku.dk:80/LaTeX/Frederiksberg/download/

This 4 may be a good starting point for customization, check out the files under 'color' directory to change theme (via Wayback Machine):

https://web.archive.org/web/20111210142341/http://staff.science.uva.nl/~faolieho/index.php?fuseaction=var.beamer

The antwerpen theme is nice, and provides examples for using images.

\pgfdeclareimage[height=\textlogoheight]{uTextColor}{logo_UA_tekst_kl}%
\ifthenelse{ \boolean{beamer@dark} \OR \boolean{beamer@darktitle} }%
% then
{\pgfdeclareimage[width=\paperwidth]{uaBackgroundDark}{uaBackgroundDarkBlue}}%
%else
{}%

if it's still of interest: A template that is very similar and I think the guy that made the presentation you mentioned gave some advise...

http://www.drbunsen.org/custom-beamer-theme.html

I have ported a PowerPoint and a Powerdot theme to Beamer. They are available here.